FIG. 1 illustrates a typical cellular packet data communications network architecture, specifically, an architecture typically employed in Cellular Digital Packet Data (CDPD) and personal Air Communications Technology (pACT) networks. The network may include a pACT Data Intermediate System (PDIS) 110, a specialized router that allows a subscriber unit 120 to move among cells 140 without losing connectivity within a fixed infrastructure network such as an internet. In particular, the PDIS 110 typically provides mobility management by constructing and continuously updating a directory/routing table that maps subscriber unit IP addresses to a temporary address and channel stream that identify with which base station 130 the subscriber unit 120 is currently connected. Typically, in order to communicate between two data link entities, for example, two subscriber units 120 or a subscriber unit 120 and PDIS 110, a data link is established between the entities over which frames or packets are communicated, with intermediate links between the subscriber unit 120, base station 130 and PDIS 110 being transparent to the entities on the ends of the data link.
Wireless environments can present several challenges to designers of communications systems, including limited bandwidth and extreme fading environments. In extreme fading environments, subscriber units may temporarily be unable to acquire signals transmitted by base stations or base stations may be unable to acquire signals from subscriber units, rendering two data link entities connected over an airlink unable to communicate. In conventional systems, if contact between subscriber unit and base station is lost for a long enough period of time, the transmitting entity typically declares the connection failed and takes action to attempt to re-establish the connection. An example of a conventional data link protocol which re-establishes a data link after transmission failure is the Mobile Data Link Protocol (MDLP) used in CDPD and pACT systems, as described in the CDPD System Specification, Release 1.1, published by CDPD Forum, Inc., Jan. 19, 1995, the disclosure of which is herein incorporated by reference in its entirety. MDLP strives to re-establish the data link connection as soon as frame delivery fails, that is, after the transmitting entity has performed a defined number of attempts to deliver a frame without receiving acknowledgment from the receiving entity. Reestablishment of the link typically requires a relatively complex handshaking procedure including the transmission of various supervisory messages. Given that a failed data link connection probably has been poor for a relatively long period of time before re-establishment is attempted, data link re-establishment will likely also fail, thus possibly wasting valuable bandwidth which could have been otherwise utilized to transport revenue-bearing traffic.